<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>下拉菜单</title>
    <style>
        *{
            padding: 0;
            margin: 0;
        }
        a{
            text-decoration: none;
        }
        li{
            list-style: none;
        }
        .nav{
            width: 100px;
        }
        .nav a{
            width: 100px;
            height: 60px;
            display: inline-block;
            line-height: 60px;
            padding-left: 25px;
            background-color: turquoise;
            color: white;
        }
        .nav .nav1{
            width: 100px;
            background-color: teal;
            padding-left: 25px;
            line-height: 60px;
            overflow: hidden;
            height: 0;
            color: white;
        }
        .nav:hover .nav1{
            height: 180px;
            transition: 0.5s;
        }
    </style>
</head>
<body>
    <div class="nav">
        <a href="#" class="home">首页</a>
        <ul class="nav1">
            <li>第一栏</li>
            <li>第二栏</li>
            <li>第三栏</li>
        </ul>
    </div>
</body>
</html>